This is the only pair of headphones I bought that I was never able to warm up to. The reason for this is that the mids - especially vocals - take on an unnatural, artificial and plasticky sound. They never sounded true to life and began to grate on me after short listening periods. They were OK for instrumental music, but even then, the tonality was off in the mids.
What's disappointing is that AKG dropped the K-501 and K-1000, and gave us this. The K-701/2 is nothing like AKG's previous efforts. I have the K-1000, K-340 and K-240DF, and used to have the K-501. All of those got the midrange right. I was expecting to love the K-701 as well, but like I said, the artificial...

I have had this set of cans around two years and it is already failing. I delicately tried to take the unit apart to repair it (I am very handy with a soldering iron) and I failed to get the unit disassembled. Fortunately for me, the act of trying to disassemble the unit fixed the problem. This leads me to believe it was a bad solder joint. Others have complained about this problem. For ~$500 I expect the cans to last at least 10 years, like my much cheaper Sennheisers. Also, the plastic parts of the headband broke within a year although this had no significant effect.
Update: After finally getting them apart, and having to cosmetically damage them...